Implementing a secondary storage dentry cache

ABSTRACT

A computer-implemented method according to one embodiment includes identifying an accessing of a file within an operating system, checking an in-memory cache for path information associated with the file, checking an external cache for the path information associated with the file, conditionally retrieving the path information associated with the file by performing a file system lookup and adding the path information associated with the file to the in-memory cache and the external cache, returning the path information, and reorganizing the external cache to put file information that is frequently accessed together in a single block or adjacent blocks.

BACKGROUND

The present invention relates to file access, and more specifically,this invention relates to performing lookups utilizing a virtual filesystem (VFS).

In predetermined operating systems (e.g., UNIX-like operating systems,etc.), when a file is accessed by a user for the first time the virtualfile system (VFS) layer may go through each component of the file pathand may construct dentry objects that tie the path components to thecorresponding inodes. This procedure is called a lookup. Current lookupoperations require multiple I/O requests to the underlying slow storage.E.g., to lookup “/tmp/foo/bar”, three or more I/O requests may be needed(one for every path component).

As a result, lookups are slow and the cost of lookup is a dominant costfor many file system instances. Current attempts to address these issueshave high memory cost and expansion size limitations.

SUMMARY

A computer-implemented method according to one embodiment includesidentifying an accessing of a file within an operating system, checkingan in-memory cache for path information associated with the file,checking an external cache for the path information associated with thefile, conditionally retrieving the path information associated with thefile by performing a file system lookup and adding the path informationassociated with the file to the in-memory cache and the external cache,returning the path information, and reorganizing the external cache toput file information that is frequently accessed together in a singleblock or adjacent blocks.

According to another embodiment, a computer program product forimplementing a secondary storage dentry cache includes a computerreadable storage medium having program instructions embodied therewith,wherein the computer readable storage medium is not a transitory signalper se, and where the program instructions are executable by a processorto cause the processor to perform a method comprising identifying anaccessing of a file within an operating system, utilizing the processor,checking an in-memory cache for path information associated with thefile, utilizing the processor, checking an external cache for the pathinformation associated with the file, utilizing the processor,conditionally retrieving the path information associated with the fileby performing a file system lookup and adding the path informationassociated with the file to the in-memory cache and the external cache,utilizing the processor, returning the path information, utilizing theprocessor, and reorganizing the external cache to put file informationthat is frequently accessed together in a single block or adjacentblocks, utilizing the processor.

A system according to another embodiment includes a processor, and logicintegrated with the processor, executable by the processor, orintegrated with and executable by the processor, where logic isconfigured to identify an accessing of a file within an operatingsystem, check an in-memory cache for path information associated withthe file, check an external cache for the path information associatedwith the file, conditionally retrieve the path information associatedwith the file by performing a file system lookup and add the pathinformation associated with the file to the in-memory cache and theexternal cache, return the path information, and reorganize the externalcache to put file information that is frequently accessed together in asingle block or adjacent blocks.

Other aspects and embodiments of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a network architecture, in accordance with oneembodiment.

FIG. 2 shows a representative hardware environment that may beassociated with the servers and/or clients of FIG. 1, in accordance withone embodiment.

FIG. 3 illustrates a tiered data storage system in accordance with oneembodiment.

FIG. 4 illustrates a method for implementing a secondary storage dentrycache, in accordance with one embodiment.

FIG. 5 illustrates an exemplary lookup environment, in accordance withone embodiment.

FIG. 6 illustrates an exemplary external cache, in accordance with oneembodiment.

FIG. 7 illustrates a method for performing dynamic reshuffling, inaccordance with one embodiment.

FIG. 8 illustrates a method for performing cache warm-up, in accordancewith one embodiment.

DETAILED DESCRIPTION

The following description discloses several preferred embodiments ofsystems, methods and computer program products for implementing asecondary storage dentry cache. Various embodiments provide a method tocheck an external cache, in addition to in-memory cache, for pathinformation when a file is accessed.

The following description is made for the purpose of illustrating thegeneral principles of the present invention and is not meant to limitthe inventive concepts claimed herein. Further, particular featuresdescribed herein can be used in combination with other describedfeatures in each of the various possible combinations and permutations.

Unless otherwise specifically defined herein, all terms are to be giventheir broadest possible interpretation including meanings implied fromthe specification as well as meanings understood by those skilled in theart and/or as defined in dictionaries, treatises, etc.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless otherwise specified. It will be further understood thatthe terms “includes” and/or “comprising,” when used in thisspecification, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

The following description discloses several preferred embodiments ofsystems, methods and computer program products for implementing asecondary storage dentry cache.

In one general embodiment, a computer-implemented method includesidentifying an accessing of a file within an operating system, checkingan in-memory cache for path information associated with the file,checking an external cache for the path information associated with thefile, conditionally retrieving the path information associated with thefile by performing a file system lookup and adding the path informationassociated with the file to the in-memory cache and the external cache,and returning the path information.

In another general embodiment, a computer program product forimplementing a secondary storage dentry cache includes a computerreadable storage medium having program instructions embodied therewith,wherein the computer readable storage medium is not a transitory signalper se, and where the program instructions are executable by a processorto cause the processor to perform a method comprising identifying anaccessing of a file within an operating system, utilizing the processor,checking an in-memory cache for path information associated with thefile, utilizing the processor, checking an external cache for the pathinformation associated with the file, utilizing the processor,conditionally retrieving the path information associated with the fileby performing a file system lookup and adding the path informationassociated with the file to the in-memory cache and the external cache,utilizing the processor, and returning the path information, utilizingthe processor.

In another general embodiment, a system includes a processor, and logicintegrated with the processor, executable by the processor, orintegrated with and executable by the processor, where logic isconfigured to identify an accessing of a file within an operatingsystem, check an in-memory cache for path information associated withthe file, check an external cache for the path information associatedwith the file, conditionally retrieve the path information associatedwith the file by performing a file system lookup and add the pathinformation associated with the file to the in-memory cache and theexternal cache, and return the path information.

FIG. 1 illustrates an architecture 100, in accordance with oneembodiment. As shown in FIG. 1, a plurality of remote networks 102 areprovided including a first remote network 104 and a second remotenetwork 106. A gateway 101 may be coupled between the remote networks102 and a proximate network 108. In the context of the presentarchitecture 100, the networks 104, 106 may each take any formincluding, but not limited to a LAN, a WAN such as the Internet, publicswitched telephone network (PSTN), internal telephone network, etc.

In use, the gateway 101 serves as an entrance point from the remotenetworks 102 to the proximate network 108. As such, the gateway 101 mayfunction as a router, which is capable of directing a given packet ofdata that arrives at the gateway 101, and a switch, which furnishes theactual path in and out of the gateway 101 for a given packet.

Further included is at least one data server 114 coupled to theproximate network 108, and which is accessible from the remote networks102 via the gateway 101. It should be noted that the data server(s) 114may include any type of computing device/groupware. Coupled to each dataserver 114 is a plurality of user devices 116. User devices 116 may alsobe connected directly through one of the networks 104, 106, 108. Suchuser devices 116 may include a desktop computer, lap-top computer,hand-held computer, printer or any other type of logic. It should benoted that a user device 111 may also be directly coupled to any of thenetworks, in one embodiment.

A peripheral 120 or series of peripherals 120, e.g., facsimile machines,printers, networked and/or local storage units or systems, etc., may becoupled to one or more of the networks 104, 106, 108. It should be notedthat databases and/or additional components may be utilized with, orintegrated into, any type of network element coupled to the networks104, 106, 108. In the context of the present description, a networkelement may refer to any component of a network.

According to some approaches, methods and systems described herein maybe implemented with and/or on virtual systems and/or systems whichemulate one or more other systems, such as a UNIX system which emulatesan IBM z/OS environment, a UNIX system which virtually hosts a MICROSOFTWINDOWS environment, a MICROSOFT WINDOWS system which emulates an IBMz/OS environment, etc. This virtualization and/or emulation may beenhanced through the use of VMWARE software, in some embodiments.

In more approaches, one or more networks 104, 106, 108, may represent acluster of systems commonly referred to as a “cloud.” In cloudcomputing, shared resources, such as processing power, peripherals,software, data, servers, etc., are provided to any system in the cloudin an on-demand relationship, thereby allowing access and distributionof services across many computing systems. Cloud computing typicallyinvolves an Internet connection between the systems operating in thecloud, but other techniques of connecting the systems may also be used.

FIG. 2 shows a representative hardware environment associated with auser device 116 and/or server 114 of FIG. 1, in accordance with oneembodiment. Such figure illustrates a typical hardware configuration ofa workstation having a central processing unit 210, such as amicroprocessor, and a number of other units interconnected via a systembus 212.

The workstation shown in FIG. 2 includes a Random Access Memory (RAM)214, Read Only Memory (ROM) 216, an I/O adapter 218 for connectingperipheral devices such as disk storage units 220 to the bus 212, a userinterface adapter 222 for connecting a keyboard 224, a mouse 226, aspeaker 228, a microphone 232, and/or other user interface devices suchas a touch screen and a digital camera (not shown) to the bus 212,communication adapter 234 for connecting the workstation to acommunication network 235 (e.g., a data processing network) and adisplay adapter 236 for connecting the bus 212 to a display device 238.

The workstation may have resident thereon an operating system such asthe Microsoft Windows® Operating System (OS), a MAC OS, a UNIX OS, etc.It will be appreciated that a preferred embodiment may also beimplemented on platforms and operating systems other than thosementioned. A preferred embodiment may be written using XML, C, and/orC++ language, or other programming languages, along with an objectoriented programming methodology. Object oriented programming (OOP),which has become increasingly used to develop complex applications, maybe used.

Now referring to FIG. 3, a storage system 300 is shown according to oneembodiment. Note that some of the elements shown in FIG. 3 may beimplemented as hardware and/or software, according to variousembodiments. The storage system 300 may include a storage system manager312 for communicating with a plurality of media on at least one higherstorage tier 302 and at least one lower storage tier 306. The higherstorage tier(s) 302 preferably may include one or more random accessand/or direct access media 304, such as hard disks in hard disk drives(HDDs), nonvolatile memory (NVM), solid state memory in solid statedrives (SSDs), flash memory, SSD arrays, flash memory arrays, etc.,and/or others noted herein or known in the art. The lower storagetier(s) 306 may preferably include one or more lower performing storagemedia 308, including sequential access media such as magnetic tape intape drives and/or optical media, slower accessing HDDs, sloweraccessing SSDs, etc., and/or others noted herein or known in the art.One or more additional storage tiers 316 may include any combination ofstorage memory media as desired by a designer of the system 300. Also,any of the higher storage tiers 302 and/or the lower storage tiers 306may include some combination of storage devices and/or storage media.

The storage system manager 312 may communicate with the storage media304, 308 on the higher storage tier(s) 302 and lower storage tier(s) 306through a network 310, such as a storage area network (SAN), as shown inFIG. 3, or some other suitable network type. The storage system manager312 may also communicate with one or more host systems (not shown)through a host interface 314, which may or may not be a part of thestorage system manager 312. The storage system manager 312 and/or anyother component of the storage system 300 may be implemented in hardwareand/or software, and may make use of a processor (not shown) forexecuting commands of a type known in the art, such as a centralprocessing unit (CPU), a field programmable gate array (FPGA), anapplication specific integrated circuit (ASIC), etc. Of course, anyarrangement of a storage system may be used, as will be apparent tothose of skill in the art upon reading the present description.

In more embodiments, the storage system 300 may include any number ofdata storage tiers, and may include the same or different storage memorymedia within each storage tier. For example, each data storage tier mayinclude the same type of storage memory media, such as HDDs, SSDs,sequential access media (tape in tape drives, optical disk in opticaldisk drives, etc.), direct access media (CD-ROM, DVD-ROM, etc.), or anycombination of media storage types. In one such configuration, a higherstorage tier 302, may include a majority of SSD storage media forstoring data in a higher performing storage environment, and remainingstorage tiers, including lower storage tier 306 and additional storagetiers 316 may include any combination of SSDs, HDDs, tape drives, etc.,for storing data in a lower performing storage environment. In this way,more frequently accessed data, data having a higher priority, dataneeding to be accessed more quickly, etc., may be stored to the higherstorage tier 302, while data not having one of these attributes may bestored to the additional storage tiers 316, including lower storage tier306. Of course, one of skill in the art, upon reading the presentdescriptions, may devise many other combinations of storage media typesto implement into different storage schemes, according to theembodiments presented herein.

According to some embodiments, the storage system (such as 300) mayinclude logic configured to receive a request to open a data set, logicconfigured to determine if the requested data set is stored to a lowerstorage tier 306 of a tiered data storage system 300 in multipleassociated portions, logic configured to move each associated portion ofthe requested data set to a higher storage tier 302 of the tiered datastorage system 300, and logic configured to assemble the requested dataset on the higher storage tier 302 of the tiered data storage system 300from the associated portions.

Of course, this logic may be implemented as a method on any deviceand/or system or as a computer program product, according to variousembodiments.

Now referring to FIG. 4, a flowchart of a method 400 is shown accordingto one embodiment. The method 400 may be performed in accordance withthe present invention in any of the environments depicted in FIGS. 1-3and 5-6, among others, in various embodiments. Of course, more or lessoperations than those specifically described in FIG. 4 may be includedin method 400, as would be understood by one of skill in the art uponreading the present descriptions.

Each of the steps of the method 400 may be performed by any suitablecomponent of the operating environment. For example, in variousembodiments, the method 400 may be partially or entirely performed byone or more servers, computers, or some other device having one or moreprocessors therein. The processor, e.g., processing circuit(s), chip(s),and/or module(s) implemented in hardware and/or software, and preferablyhaving at least one hardware component may be utilized in any device toperform one or more steps of the method 400. Illustrative processorsinclude, but are not limited to, a central processing unit (CPU), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA), etc., combinations thereof, or any other suitablecomputing device known in the art.

As shown in FIG. 4, method 400 may initiate with operation 402, where anaccessing of a file within an operating system is identified. In oneembodiment, the accessing may include the performing of an operation onthe file (e.g., a read, a write, a metadata update, etc.). In anotherembodiment, the operating system may include a Unix®-based operatingsystem or a Unix®-like operating system (e.g., a Linux®-based operatingsystem, etc.). In yet another embodiment, the identifying may beperformed by a virtual file system (VFS) within a hardware computingdevice.

Additionally, as shown in FIG. 4, method 400 may proceed with operation404, where an in-memory cache is checked for path information associatedwith the file. In one embodiment, the in-memory cache may includenon-persistent memory within a system. For example, the in-memory cachemay include random access memory (RAM) within the system. In anotherembodiment, the in-memory cache may store previously determined pathinformation. For example, the in-memory cache may include pathinformation determined during past lookups. In yet another embodiment,the in-memory cache may include an in-memory directory entry (dentry)cache.

Further, in one embodiment, the path information may include a dentryobject for each component of the file path. For example, dentry objectsmay tie path components to corresponding inodes. In another embodiment,the VFS may detect when the file is accessed by the user and mayconstruct directory entry (dentry) objects that tie path components toinodes within the system.

In another embodiment, the path information may include an inode. Forexample, the inode may include a data structure that stores metadatadescribing an object (e.g., the file, one or more directories containingthe file, etc.). For instance, the inode of the file may includeattributes of the file, a location of the file within one or more diskblocks, etc.

Further still, in one embodiment, the checking of the in-memory cachemay be performed by the VFS. For example, the checking may be done aspart of a lookup operation in response to the accessing of the file, aspart of a translation of the file to an inode, etc.

Also, as shown in FIG. 4, method 400 may proceed with operation 406,where an external cache is checked for the path information associatedwith the file. In one embodiment, the external cache may be checked upondetermining that the in-memory cache does not contain the pathinformation associated with the file. In another embodiment, theexternal cache may be checked in parallel with the in-memory cache.

In addition, in one embodiment, the external cache may be local (e.g.,included in the system containing the in-memory cache), or may beincluded in a device separate from the system containing the in-memorycache. For example, the external cache may be included in a dcachedevice separate from a main system device that contains the in-memorycache. In another embodiment, the external cache may include persistentmemory. For example, the external cache may include flash memory, asolid state drive (SSD), etc. In yet another embodiment, the externalcache may include an external dentry cache.

Furthermore, in one embodiment, the external cache may contain a mappingof an entire path to an inode for the file. This may enable thetranslation of the file to an inode in a single input/output (I/O)operation. In this way, lookup performance may be improved. In anotherembodiment, in-memory cache may be populated from the external cacheduring a reboot.

Further still, in one embodiment, the checking of the external cache maybe performed by the VFS. For example, the checking may be done as partof a lookup operation in response to the accessing of the file, as partof a translation of the file to an inode, etc. In another embodiment,the in-memory cache and the external cache may be populated in responseto file access by one or more users.

Also, as shown in FIG. 4, method 400 may proceed with operation 408,where the path information associated with the file is conditionallyretrieved by performing a file system lookup and added to the in-memorycache and the external cache. In one embodiment, the path informationmay be retrieved by performing the file system lookup and added to thecaches upon determining that the path associated with the file is notfound in either the in-memory cache or the external cache. For example,the file system lookup may be performed by constructing dentry objectsfor each component of the path for the file, where the dentry objectstie the path components to the corresponding inodes. In anotherembodiment, the file system lookup may include performing one or moreI/O requests to disk storage. In another embodiment, the disk storagemay include a hard disk drive (HDD) within the system. In yet anotherembodiment, the data retrieval from the disk storage may be slower thandata retrieval from the external cache.

Additionally, in one embodiment, the retrieving of the path informationmay be performed by the VFS. In another embodiment, the path informationretrieved as a result of the file system lookup may be stored in thein-memory cache as well as the external cache.

Further, as shown in FIG. 4, method 400 may proceed with operation 410,where the path information is returned. In one embodiment, the pathinformation may be returned by the VFS to the operating system. Inanother embodiment, returning the path information may include returningan inode for the file. For example, the inode may be used by theoperating system to access the file. More specifically, metadata fromthe inode may be used to determine a location of stored datarepresenting the file. In yet another embodiment, when it is determinedthat the path associated with the file is not found in either thein-memory cache or the external cache, a file system lookup may beperformed, and information from the lookup may be added to one or moreof the in-memory cache and the external cache.

Further still, in one embodiment, the VFS may be modified to check forentries in the external cache. For example, the operating system mayimplement a VFS to abstract access to specific file systems. The VFS mayalso be modified to allow file lookups without looking up individualpath components. For example, a lookup method may be called with acomplete file path as an argument. In another embodiment, one or moreinternal non-looked-up dentries may be implemented for intermediatecomponents of a path. For example, the internal non-looked-up dentriesmay correspond to directories on which a lookup was not performed, butwhere a lookup was performed on files in those directories.

Also, in one embodiment, the VFS may be bypassed, and the file systemmay be implemented at a system call level. In another embodiment, theexternal cache may be implemented using a stackable file system to avoidkernel modifications. In yet another embodiment, the external cache maybe generic, such that each of a plurality of different file systems mayutilize the external cache.

In this way, in-memory cache may be extended to an external cache insecondary storage.

To reduce lookup times, operating systems may cache dentries and inodesin an in-memory dentry cache in the main memory of a system. The dentrycache may be implemented as a hash table that maps a (parent_inode,“child_name”) tuple to the inode.

In one embodiment, a file system may maintain a hierarchy ofdirectories. E.g., in Unix®, file F may be located in directory D, whichin turn is in directory C, which is in directory B, which is in A.Conventionally, such path may be designated as /A/B/C/D/F. In anotherembodiment, to perform an operation on file F (e.g., read/write the dataor perform metadata update), traditional file systems may firsttranslate the path (e.g., /A/B/C/D/F) to the inode (also called avnode), which may contain metadata for the file, including the locationsof data blocks for the file in data storage. The procedure oftranslating file path to inode is called a lookup.

Additionally, in one embodiment, performing the lookup may be enhancedby caching lookup results on an external cache (e.g., a secondarystorage device such as an SSD, etc). This external cache may include anauxiliary dentry cache and may reside on a dcache device. In anotherembodiment, the external cache may be reorganized to put fileinformation that is frequently accessed together in a single block oradjacent blocks. In yet another embodiment, the external cache may bepre-populated proactively from a file system as a background process.

FIG. 5 illustrates an exemplary lookup environment 500, according to oneembodiment. As shown, the environment 500 includes in-memory dentrycache 502, an external dentry cache 504 included within a dcache device506, and disk storage 508.

In one embodiment, during a lookup, a VFS may first check the in-memorydentry cache 502. In case of a miss at the in-memory dentry cache 502(e.g., where the in-memory dentry cache 502 does not return the desiredpath information), the VFS may then check the entries in the externaldentry cache 504 at the dcache device 506. If the desired pathinformation is found, then a corresponding inode is returned by theexternal dentry cache 504 to the VFS.

Further, in one embodiment, if the path is not found (e.g., where theexternal dentry cache 504 does not return the desired path information),then an underlying file system lookup (e.g., Ext4, XFS, etc.) isperformed. For example, the file system lookup may include performingone or more I/O requests to disk storage 508. In another example, for/A/B/C/D/F, first A is looked up in the root directory, then B is lookedup in A, then C is looked up in B, D is looked up in C, and finally F islooked up in D. Every I/O request may read one or more directory blocksthat contain directory entries. Directory entries may describe the filenames and inodes (or inode numbers) of the files residing in thisdirectory.

Further still, in one embodiment, after the underlying file systemlookup is performed, the retrieved entries may be put both in thein-memory and secondary dentry cache. In one embodiment, the lookup onthe in-memory dentry cache 502 and in the external dentry cache 504 maybe performed in parallel. Unlike in-memory dentry cache, the dcachedevice 506 may be organized as a mapping of the whole path to the inode.

FIG. 6 illustrates an exemplary external cache 600, according to oneembodiment. As shown, the external cache 600 includes a plurality ofentries 602A-N, where each of the plurality of entries 602A-N includes amapping of an entire path to an inode. For example, entry 602C includesa mapping of the entire path “/A/B/C/D/F” to an inode.

In this way, a translation of arbitrarily deep files names to inodes maybe made in a single I/O operation, which may increase the performance ofa lookup operation. For example, in one embodiment, an on-disk hashtable may be used for storing the entries, and a single I/O operationmay bring the whole bucket to the memory.

Additionally, in one embodiment, Unix® systems may implement a VFS layerwhich may abstract access to specific file systems. In anotherembodiment, the VFS may be modified to check for entries in the externalcache 600. This may allow any existing file system to reap the benefitsof fast cached lookups.

Further, in one embodiment, the VFS may be modified to allow filelookups without looking up individual path components. For example, thelookup method may be called with a complete file path as an argument. Inanother embodiment, internal non-looked-up dentries may be introducedfor the intermediate components of the path (e.g., A, B, C, and Din/A/B/C/D/F) because they may not need to be looked up when file F isopened.

Further still, in one embodiment, the VFS may be completely bypassed anda file system may be implemented at a system call level. In anotherembodiment, a stackable file system may implement the lookups to avoidkernel modifications.

Also, in one embodiment, when files and directories are renamed orremoved, corresponding entries in the cache may need to be updated. Inanother embodiment, this may be achieved by a simple invalidation of allaffected entries within the external cache 600. In yet anotherembodiment, the new names of renamed files may be rehashed within theexternal cache 600, and inodes may be moved to the new locations.

In addition, in one embodiment, when a directory rename happens, themappings for all files that belong to the directory may be updatedwithin the external cache 600. In another embodiment, only thedirectories with a number of files less than a predetermined thresholdmay be cached. This may allow for a limitation of an overhead associatedwith renames. In another embodiment, only the directories with a numberof path components less than a predetermined threshold may be cached.

Furthermore, in one embodiment, the external cache 600 may either cacheinode numbers or complete inodes (e.g., based on one or more userrequirements, etc.). In another embodiment, in addition to the inodeinformation, the external cache 600 may store access control informationfor the whole path. For example, the access control information may beused to decide if the lookup is allowed for a specific user process. Inyet another embodiment, when file or directory permissions or ownershipchanges, corresponding cache entries within the external cache 600 maybe invalidated or updated in a manner similar to renaming.

Further still, in one embodiment, the external cache 600 may beconfigured to store negative dentries (e.g., information about the filesthat do not exist, etc.). Depending on the workload, a correspondingparameter may be set on or off.

Now referring to FIG. 7, a flowchart of a method 700 for performingdynamic reshuffling is shown according to one embodiment. The method 700may be performed in accordance with the present invention in any of theenvironments depicted in FIGS. 1-3 and 5-6, among others, in variousembodiments. Of course, more or less operations than those specificallydescribed in FIG. 7 may be included in method 700, as would beunderstood by one of skill in the art upon reading the presentdescriptions.

Each of the steps of the method 700 may be performed by any suitablecomponent of the operating environment. For example, in variousembodiments, the method 700 may be partially or entirely performed byone or more servers, computers, or some other device having one or moreprocessors therein. The processor, e.g., processing circuit(s), chip(s),and/or module(s) implemented in hardware and/or software, and preferablyhaving at least one hardware component may be utilized in any device toperform one or more steps of the method 700. Illustrative processorsinclude, but are not limited to, a central processing unit (CPU), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA), etc., combinations thereof, or any other suitablecomputing device known in the art.

As shown in FIG. 7, method 700 may initiate with operation 702, wherepatterns in file access are monitored by an external cache. In oneembodiment, the patterns may include the accessing of one or moreadditional files after initial access of a first file. Additionally,method 700 may proceed with operation 704, where it is determined that asecond file is likely to be accessed within a predetermined time afterthe accessing of a first file, based on the monitoring.

Further, method 700 may proceed with operation 706, where pathinformation associated with the first file is placed adjacent to pathinformation associated with a second file, in response to thedetermination. For example, entries for files that are frequentlyaccessed together may be placed in the same or adjacent blocks, so thatthose file entries are brought in memory together. In one embodiment,each entry may include a directory entry including path informationassociated with a file.

In this way, a single I/O operation may bring into an in-memory cache aplurality of directory entries that are likely to be accessed within apredetermined time of each other.

Further, in one embodiment, a prediction may be made as to what filesare likely to be accessed based on one or more environmental variables(e.g., process names, user names, etc.), and the directory entries inthe external cache may be reshuffled based on the prediction. In anotherembodiment, information may be proactively requested from the mainsystem. In yet another embodiment, one or more directory entries may beproactively pushed from the external cache into the in-memory cache.

Further still, in one embodiment, file access patterns may bepredictable. For example, when a specific file is accessed there may bean increased chance that a specific subset of other files will beaccessed shortly. The external cache may monitor such patterns and mayreshuffle directory entries on the external storage device so that asingle I/O operation may bring into memory many directory entries thatwill be accessed within a predetermined time period. In anotherembodiment, environmental hints (e.g., process and user names) may beused to detect which files are likely to be accessed soon.

Also, in one embodiment, using this mechanism, the external cache mayalso proactively request directory entries from the main file systemdevice and may also push the entries to the in-memory dentry cache.

Now referring to FIG. 8, a flowchart of a method 800 for performingcache warm-up is shown according to one embodiment. The method 800 maybe performed in accordance with the present invention in any of theenvironments depicted in FIGS. 1-3 and 5-6, among others, in variousembodiments. Of course, more or less operations than those specificallydescribed in FIG. 8 may be included in method 800, as would beunderstood by one of skill in the art upon reading the presentdescriptions.

Each of the steps of the method 800 may be performed by any suitablecomponent of the operating environment. For example, in variousembodiments, the method 800 may be partially or entirely performed byone or more servers, computers, or some other device having one or moreprocessors therein. The processor, e.g., processing circuit(s), chip(s),and/or module(s) implemented in hardware and/or software, and preferablyhaving at least one hardware component may be utilized in any device toperform one or more steps of the method 800. Illustrative processorsinclude, but are not limited to, a central processing unit (CPU), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA), etc., combinations thereof, or any other suitablecomputing device known in the art.

As shown in FIG. 8, method 800 may initiate with operation 802, where asystem boot event is identified. In one embodiment, the system bootevent may include a booting of the system, a rebooting of the system,etc. Additionally, method 800 may proceed with operation 804, where pathinformation in an in-memory cache of the system is restored, utilizingan external cache.

In one embodiment, the path information may be transferred from theexternal cache to the in-memory cache. In another embodiment, the pathinformation may be transferred utilizing sequential I/O operations tostream the path information from the external cache to the in-memorycache. In this way, persistent memory in the external cache may be usedto restore (e.g., “warm up”) non-persistent memory in the in-memorycache.

In this way, in-memory dentry cache may be extended to secondarystorage. In addition to keeping dentries and inodes in main memory(e.g., in an in-memory cache), a VFS may keep path-to-inode mappings onan external storage device (e.g., an external cache in a dcache device).In on embodiment, the dcache device may be faster than the device onwhich the file system resides (e.g., the file-system device).

Storing path-to-inode mappings on an external storage device may haveseveral advantages. For example, such storage may transparently workwith any underlying file system. Additionally, such storage may beindexed by a full path instead of by a path component, which may allowthe names to be resolved only in a single I/O irrespective of the pathlength. Further, such storage may enable I/O operations that fetch morethan single dcache entry at a time.

Further still, such storage may track user file accesses and proactivelyfetch dentries and inodes from the file-system device to the dcachedevice. Such storage may also push dentries and inodes to the in-memorydentry cache, and reshuffle dentries on the dcache drive so thatmultiple dentries that are likely to be accessed together can be broughtin-memory using a single I/O operation.

Also, after reboot, the secondary storage may allow the VFS to quicklyrepopulate in-memory dentry cache based on the most recently used ormost frequently used dentries. This may shorten the cache warmup periodfor file systems.

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein includes anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which includes one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

Moreover, a system according to various embodiments may include aprocessor and logic integrated with and/or executable by the processor,the logic being configured to perform one or more of the process stepsrecited herein. By integrated with, what is meant is that the processorhas logic embedded therewith as hardware logic, such as an applicationspecific integrated circuit (ASIC), a FPGA, etc. By executable by theprocessor, what is meant is that the logic is hardware logic; softwarelogic such as firmware, part of an operating system, part of anapplication program; etc., or some combination of hardware and softwarelogic that is accessible by the processor and configured to cause theprocessor to perform some functionality upon execution by the processor.Software logic may be stored on local and/or remote memory of any memorytype, as known in the art. Any processor known in the art may be used,such as a software processor module and/or a hardware processor such asan ASIC, a FPGA, a central processing unit (CPU), an integrated circuit(IC), a graphics processing unit (GPU), etc.

It will be clear that the various features of the foregoing systemsand/or methodologies may be combined in any way, creating a plurality ofcombinations from the descriptions presented above.

It will be further appreciated that embodiments of the present inventionmay be provided in the form of a service deployed on behalf of acustomer to offer service on demand.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of a preferred embodiment shouldnot be limited by any of the above-described exemplary embodiments, butshould be defined only in accordance with the following claims and theirequivalents.

What is claimed is:
 1. A computer-implemented method, comprising:identifying an accessing of a file within an operating system; checkingan in-memory cache for path information associated with the file;checking an external cache for the path information associated with thefile; conditionally retrieving the path information associated with thefile by performing a file system lookup and adding the path informationassociated with the file to the in-memory cache and the external cache;returning the path information; and reorganizing the external cache toput file information that is frequently accessed together in a singleblock or adjacent blocks.
 2. The computer-implemented method of claim 1,wherein the in-memory cache includes non-persistent memory within asystem.
 3. The computer-implemented method of claim 1, wherein the pathinformation includes an inode that stores metadata describing a locationof the file within one or more disk blocks.
 4. The computer-implementedmethod of claim 1, wherein the external cache is checked upondetermining that the in-memory cache does not contain the pathinformation associated with the file.
 5. The computer-implemented methodof claim 1, wherein the external cache is checked in parallel with thein-memory cache.
 6. The computer-implemented method of claim 1, whereinthe in-memory cache and the external cache are populated in response tofile access by one or more users.
 7. The computer-implemented method ofclaim 1, wherein the external cache includes persistent memory.
 8. Thecomputer-implemented method of claim 1, wherein the in-memory cache ispopulated from the external cache during a reboot.
 9. Thecomputer-implemented method of claim 1, wherein the external cachecontains a mapping of an entire path to an inode for the file.
 10. Thecomputer-implemented method of claim 1, wherein the checking of theexternal cache is performed by a virtual file system (VFS) as part ofthe file system lookup in response to the accessing of the file.
 11. Thecomputer-implemented method of claim 1, wherein the external cache ispre-populated proactively from a file system as a background process.12. The computer-implemented method of claim 1, wherein the externalcache is generic, such that each of a plurality of different filesystems utilize the external cache.
 13. A computer program product forimplementing a secondary storage dentry cache, the computer programproduct comprising a computer readable storage medium having programinstructions embodied therewith, wherein the computer readable storagemedium is not a transitory signal per se, the program instructionsexecutable by a processor to cause the processor to perform a methodcomprising: identifying an accessing of a file within an operatingsystem, utilizing the processor; checking an in-memory cache for pathinformation associated with the file, utilizing the processor; checkingan external cache for the path information associated with the file,utilizing the processor; conditionally retrieving the path informationassociated with the file by performing a file system lookup and addingthe path information associated with the file to the in-memory cache andthe external cache, utilizing the processor; returning the pathinformation, utilizing the processor; and reorganizing the externalcache to put file information that is frequently accessed together in asingle block or adjacent blocks, utilizing the processor.
 14. Thecomputer program product of claim 13, wherein the in-memory cacheincludes non-persistent memory within a system.
 15. The computer programproduct of claim 13, wherein the path information includes an inode thatstores metadata describing a location of the file within one or moredisk blocks.
 16. The computer program product of claim 13, wherein theexternal cache is checked upon determining that the in-memory cache doesnot contain the path information associated with the file.
 17. Thecomputer program product of claim 13, wherein the external cache ischecked in parallel with the in-memory cache.
 18. The computer programproduct of claim 13, wherein the in-memory cache and the external cacheare populated in response to file access by one or more users.
 19. Thecomputer program product of claim 13, wherein the external cacheincludes persistent memory.
 20. A system, comprising: a processor; andlogic integrated with the processor, executable by the processor, orintegrated with and executable by the processor, the logic beingconfigured to: identify an accessing of a file within an operatingsystem; check an in-memory cache for path information associated withthe file; check an external cache for the path information associatedwith the file; conditionally retrieve the path information associatedwith the file by performing a file system lookup and add the pathinformation associated with the file to the in-memory cache and theexternal cache; return the path information; and reorganize the externalcache to put file information that is frequently accessed together in asingle block or adjacent blocks.